Multiplex signaling system



May 12, 1925. 1,537,154

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Patented May 12, 1925.

UNITED STATES P rsivr ori-ics WALLACE V. lViI'OLFE, OF CORONA, NEW YORK,ASSIGN'OR' TO yWNESTE".Lfll' ELECTRC COMPANY, INCORPORATED, OF NEW'YORK,N. Y., A CORPORAION OF NEW YORK.

`ifiirixrirL-EX sIGNALiNe SYSTEM;

Application filed November 29, 1922. Serial No. 603,307.`

To all iii/10m 'it may concern:

Be it known that I, 'lVALLAon V. lNoLrn, a citizen of the United Statesof America, residing at Corona, in the county of Queens and State of NewYork, have invented certain new and useful Improvements in MultiplexSignaling Systems, of which the following` isa full, clear, concise, andexact description.

The present invention relates tol signaling by means of carrier waves,and more particularly to provisions for the transmission of signalsthrough a plurality of carrier wave channels constituting a multiplexsystem. f y y The invention relates particularly to the type of carriertransmission system in which the carrier wave is normally continuously7transmitted, and in which the carrier waves of the various channels maybe independently interrupted to transmit a signal over any particularchannel. In the embodiment of the` invention to be described, the normally continuously transmitted carrier waves are` modifiedor modulated totransmit one kind of signal such as speech, for example7 and aretemporarily ,interrupted to. transmit another kind of signal such as' acall signal. i lin systems of this character, sometimes teri'ned closedcircuit systems, the entire signaling circuit such as the line must beintact and the terminal apparatus must be in opeiative condition inorder that the carrier waves may `be continuously transmitted andreceived. An interruption to the transmission through the. system due,for example, to a break in the line or in a common terminal circuit, orto adverse nf'eather conditions in the case of aline system, or of aradio system, for example7 may result in an interruption ofeach. or anumber of the carrier waves beine; transmitted. and such an interruptionof all or a plurality of the received carrier waves may conveniently betaken as an indication of a failure of the system. rThisis imrticularlytrue since it is very improbable that. all or a number of the carrierwaves would be interrupted simultaneously in the normal operation .oftransmitting call signals oi'er the various channels.

lt is an object yof theinvention to provide for giving' asigiial inresponse to interruption of the carrier wares-iii a plurality ofchanni-ils simultaneously.

This signal or alarm may-be `used to indicate to an attendant a failurein the system, or ka reduced or interrupted transmission of the carriercurrents, as'will beexplained The general type of carrier current systemto which the invention is particularly applicable, is shown anddescribed in an article entitled Carrier'current telephony andtelegraphy by E. H. Colpitts and O. B. Blackwell,,beginning inthei-rpril7 192i Journal of the American Institute of ElectricalEngineers, at page 420, Fig. 42.

The drawing` to which the following` description refers illustratesdiagrammatically a system of the type shown inthe Golpitts and Blackwellarticle with an embodiment of the invention'incorporated therein.y

Referring to the drawing, the line ML may be a multiplex carrier currentline and the line LLmay be one of a. plurality of low frequency linessuch as ordinary subscriloers7 loops arranged for two-way repeating` toand from the carrier line. The main line, or carrier line, is providedwith. a balancingnetwork MN and a conjugate repeating` coil, or hybridcoil, H, having a transmittingloop TL and a receiving loop RL associatedwith the hybrid coil and conjugately related to each other, Each lowfrequency line is also provided with a balancing network LN and a hybridcoil as shown, having conjugate branches for respectively iii/ipressingcurrents on the line LL'and ,deriving currents therefrom.

Each branch or repeating` circuit for repeating signals from the lowfrequency line to the high frequency line comprises a modulator such asM1 normally suppliedh with carrier current from a source such as S, anda band filter such as BF, for selectively transmitting to thetransmission loop TL the range of frequencies setaside for the exclusiveuse of the particular channel. The repeating circuit for. transmittingfrom the high frequency line to a low frequency line such as LLcomprises a band filter such- `as BFL adapte/dito transmit selectivelythe "ange of frequencies used exclusively bv this channeL-a detector ordemodulator DM, and a low frequency or speech frequency filter LF forconfining the currents transmitted to the line LL to the voice frequencyrange. Also associated with the output side of the demodulator DM'l is ahigh frequency iilter HF, selective of the carrier frequency,

and a rectifier R for su i vilvine the rectified i a y lun carrierfrequency current to a control relay 10. Each of the filters BFl, HFl,LF and BF4k may be of the type described in the Colpitts and Blackwellpaper referred to and more fully disclosed in the patent to G. A.Campbell No. 1,227 ,113, issued May 22, 1917. The modulator M1 and therectifier R1 are preferably of the vacuum tube type such as areindicated in Fig. 42 of the Colpitts and Blackwell paper referred to.Also the carrier frequency source indicated at S is preferably of thevacuum tube type having a regenerative connection for causing thecontinuous production of oscillations, although this source may be ofany other suitable type suchv as a machine generator.

The filter BF2 and the demodulator DMg are assumed to comprise thereceiving side of a second carrier channel leading to a second loivfrequency line Which is not shown, but which may be entirely similar tothe line LL. This channel employs a carrier current of a frequencydifferent from that used in the channel previously described and theband filter BF2 is designed in accordance with the principles set forthin the Campbell patent referred to, so as to have a selectivetransmission range for the currents of the frequency range usedexclusively by this channel. Similarly the filter HF2 is selective ofthe carrier Wave transmitted over this particular channel. The circuitfor transmitting from the second low frequency line (not shown) to themultiplex carrier line ML by Way of the common transmission loop TL isindicated by the branch 11.

The band filter BFM demodulator DWS, filter HF,v and rectifier are in asimilar manner associated with a third low frequency line which is notshown in thc dra\ving, but which may be a duplicate of the line LL andthe circuit for transmitting from this third assumed loW frequency lineto the transmission loop TL is indicated by the connectinfr terminals12. Associated with the rectifier B2 is a relay 13 and associated withthe rectifier R3 is a relay The filters HFl, HF2 and HF3 may in eachinstance be a simple timed circuit if desired. The relay 15, which isadapted to be actuated by tlie relays 10, 13 and la in common in themanner to be described below, is pret'- erably marginal so that itsarmature is normally retracted and holds open the circuit of the alarm16, except When a current exceeding a predetermined strength is flowingin the Winding of the relay 15. The resistanccs 17, 18 and 19 may eachbe any desired type of current consuming indicating device such as alamp or an electromagnetic signal. The purpose and function of therelays 20, 21 and 22 Will appear from the description of operation ofthe system which will now be given.

The operation of the system in transmit ting speech is substantially asdescribed in the Colpitts and Blackwell paper referred to. The speechfrequency currents received from the subscribers station on the line LLare repeated into the circuit of modulator M1 where they combine withthe carrier Wave from the source S in well known mannei to produce avoice modulated high fri quency Wave. This Wave is selectively tausmitted by band filter BF* to the branch TL and to the multiplex lineML for transmission to a distant station. The manner in which the Waveis received and' again converted into speech at the distant station willbe clear from considering a similarly modulated Wave received at thestation shown. Such a Wave received -over the uppermost channel in thedrawing, for example, is selectively transmitted by the band filter BF1to the demodulator DMI, which operates in Well known manner to reproducecurrents of the speech frequency range. These currents pass selectivelythrough the low pass filter LF from which they are impressed on the lineLL.

The relay 21 bridged across the telephone line LL is made selective ofringing or signalmg current adapted to be transmitted from the distantstation on the low frequency line, but remains inert when currents ofdifferent character such as speech currents or talking currents traversethe line LL. This selectivity maybe secured in a manner Well known inthe art such as by including the condenser as shown in the circuit ofthe relay, and by proportioning the inductance of the Winding and also,if necessary, the mechanical construction of the armature. Except when aringing or calling signal is received over the line L'L, rela-y 21allows its armature to close continuously the energizing circuit for therelay Relay 22 by continuously attracting it-s armatures permits asupply of carrier current from the source S to the modulator Ml andthrough the band filter BF4 to the main line ML. Tu a similar manner itis assumed that the carrier current is normally continuously suppliedthrough the branches 11 and 12 to the line ML under control of other lowfrequency lines not shown. Similarly also at a distant terminal of themultiplex line ML, thc corresponding lou' frequency .lines with whichthe lines LL and similar lines at the station shown are adapted toconverse, are assumed to maintain normally the supply ol correspondingcarrier currents to the multiplex line ML, except when a call signal isto be transmitted. Accordingly at the station shown in the d aivingthere is normally being received continuously a sustained carrier Wavein each of the carrier channels associated With the line ML.

The carrier current normally continuously meuse' received over amvchannel such. as the upper most channel iliustrated in the drawing isselectively passed through the band filter BF, and passes into thedemodulator DM1 .Where a partial rectiiication takes place.

larly the carrier current normally received continuously over eachV ofthe other channels maintains the respective relays 13 and 111 inenergized condition.

` When it is desired totransmit a ringing or calling signal from a lovvlrequency line such as LL through the correspondingcarrier channel andout over the cooperating loW frequency at la distant station on the lineML, ringing current of the character to Which relay 21 is selectivelyresponsive is transmite-d over the line LL. Relay 21 in response to thisringing current pulls up its armature, opening the circuit of relay 22which releases its armatures. The supply ot carrier current to themodulator M1 from the source S is thus interrupted for the duration otthe calling signal received from the line LL. The etl'ect of thisinterruption or' the distant station will be understood from consideringthe effect at the station'shown ot an interruption in the carriercurrent normally continuously received.

yConsidering the uppermost chanel ot the drawing an interruption ofthe'recei-vedcarrier in this 'channel allows the relay 10 to deenergize,whereupon a circuit is closed for the relay 2O from grounded battery,Winding` of relay 20, armature and back contact ot relay 10, and thearmatureland front contact of one or all of the remaining relays 13,111-, etc. on the assumption that the cary rier Waves normally beingreceived bythese several channels Will not all be simultaneouslyinterrupted in the normal operation" of transmitting calling signals. Acircuit in shunt of the relayis also closed from that curients on theline LL can have no etlect upon the carrier terminal apparatus. Theringing current sent out over the line LL from the source 25 may serve,in accordancey with standard practice, to actuate a signal device at thedistant station ot the line LL.

In an entirely similar manner, calling or ringing signals may besimultaneously and selectively transmitted through each of the othercarrier channels by momentary inter-` `ruption or' thel respectivecarrier Wave. In

case of the simultaneous interruption of all or a number of the carrierWaves normally being received, all or a plurality o i the relays 10, 13and 14, etc., Will be simultaneously deenergized. The marginal relay 15,it will be noted, is included in a circuit in shunt to ground of thecircuit for energizing relay 2O and signal device 17. In the normaloperation of the system in transmitting a ringing current over a singleone of the channels, or over a pluralityl of channels less than apredetermined number, re-

'lay 15 will draw insuiiicient current from a path including battery andrelay 20, and battery and resistance 17 in parallel, (or a plurality ofsuch paths in parallel it' more than one channel are simultaneouslycalling) armature and back contact et one or a 'correspon-ding pluralityof relays 10, 18, etc., resistance 24, and Winding o1' relay 15 toground in parallel with one or more resistances 24, and armature andfront contact of the relays 13, 14, etc., that may still be in energizedcondition. However, if all ot the relays 10, 13, 141, etc., aresimultaneously deenergized, or il more than a pre-` determined numberare deenergized simultaneously, the current through the correspondingplurality or' relays in parallel', through the corresponding indicatingdevices 17 in parallel, and through the Wind-- ing of relay 15, will besuiiicient to energize this relay and cause it to pull up its armatureto actuate the alarm signal 1G. For ere ample, in a live channel systemthe resistances 17, 18, 19 and 24; and the impedance of the windings or'the relays 2O of the various lines may be so proportioned with respectto the characteristics ofrelay 15 that it' the Carrier current on fourof the channels is interrupted simultaneously the re- 'lay 15 willenergize, Whereas it three or less than three of the carrier Waves aresimulta- -neously interrupted, the relay 15 will receive insuificientcurrent to energize.

It three or less than three carrier Waves are interruptedsimultaneously, it follows that two ortheir carrier Waves simultaneouslyinterrupted, the resistances 1i', 8, 19, 'and the relay 15 maybe such`that none of the relays 20 1n question can be operated on account ofthe single remaining resistance 2l Cil in the single remaining groundcircuit, As explained above, however, relay l5 will under theseconditions operate. By suitable-adjustinent therefore, the system may bear- `rangedso that no ringing signal will loe sent out on any lowfrequency line LL in ease a ringing signal is siini'lltaneously receivedover a plurality of carrier channels greater than a predeterminednumber, While under these. sam-e conditions the alarm lo will beactuated. If desired, however, the system may be adjusted so thatringing signals simultaneously received over the various channels Willbe repeated over the respective lines, except in the single instanceWhenthe carriers in all of the channels are simultaneously interrupted,this being also the only condition on Which the alarm 16 is operated.rlhe invention lends itself, therefore, to various adjustmentscorrespondingto interruption of transmission on all of the channels, orto a condition of reduced transmission through the systen'i due to thecessation of current on a part of the channels only. rlhis latteradjustment may be convenient, for example, in cases Where the alarm 1Gis to be actuated to indicate a change in the transmitting conditionswhich is selective in character and etlects only the channels employingWaves of certain frequencies;

Thile the invention has been described as applied to a specific type oftransmitting system, itis to be understood that the invention isnotlimited to the particular type-of system disclosed, nor to systems inwhich the carri-cr Waves are transmitted over a conductive circuit, butthatl it is equally applicable to other types of line transmissionsystems than that disclosed and also to radio systems.

that is claimed is:

l. In a signaling system a plurality` ofY carrier Wave transmissionchannels, means to transmit signals through the respective channelscomprising means for withdrawing the respective carrier waves fromtransmission, and a signal device actuated only in a signalingdevice`and means for actuating said signaling` device in response to theconditionof withdrawal of the normally transmitted carrier wave in aplurality of said channels at the same time.

3. In a multiplex carrier signaling lsystem a. plurality of carrierchannels, means for normally continuously transmitting the carrier Wavesthrough the respective carrier channels, means for independentlytransmitting a signal through each' of said channels in response to theWithdraw-al-from transmission of the normally transmitted carrier Wave,a .signaling device, and means dependent upon the condition ofwithdrawal of the carrier Waves existing. simultaneously in a pluralityof channels in excess only of a predetermined nuniber for controllingsaid signaling device.

4. In a multiplex carrier wavesystem a plurality of distinct carrierwave transmission channels superposedr onv the same medium, means fornormally continuously tansmitting the carrier wave through each of saidchannels, a `relay foreach of said channels normally energized' inresponse to the carrier'transmitted through the respective channel, asignaling element associated with each of said relays, a signalingdevice common to said relays andmeans responsive to the deenergizationof each of said relays for actua-ting thev corresponding signalingelement and responsive only to the simultaneous deenergization of aplurality of said relays in excess of .a predetermined iniinbei'forcontrolling,actuation of said signaling z device.

5.y In a multiplex carrier Wave transmissionsystem, av Aplurality ofdistinct carrier wave transmission channels, means for transmittingsignalsithrough said respective channels, an alarm signaland meanscontrolled by carrier Waves receivedover said channels and responsive toa .failure in the `transmission system resulting in the=condition ofWithdrawal.from transmission of all of said carrier iva-vesatthesametimeffor actuating said alarm signal.

6. In a multiplex carrier wave transmission systm, means to transmitnormally and continuously a plurality of carrier waves of respectivelydifferent frequency, a corresponding plurality of signals, meansresponsive to the Withdrawal from transn'iission of a carrier Wave foractuating the corresponding signal, an iudicatingdevice and meansdependent upon the condition of Witlnlraival at the same` time of aplurality of said carrier waves for actuating saidindicatingl device.

7. In a multiplex carrier Wave transmission system', means for normallyand continuously transmitting a plurality of carrier Waves ofrespectively different frequency.` a corresponding plurality of signals,means responsive to the Withdrawalfrom transmission of a carrier wavefor actuating the corresponding signahmeans responsive `to the conditionof withdrawal at thesame time of a plurality of said carrier Waves forpre- CII llltl lfll) 8. In a multiplex carrier Wave signaling system,means for normally continuously transmitting al pluralityof carrierWaves of respectively different frequency, a plurality of receivingcircuits for the respective carrier Waves, interlocking circuitsbetweenk said receiving circuits, a plurality of signals each having acircuit controlled in the interlocking circuits of said receivingcircuits, a marginal relay also controlled in said interlockingcircuits, means responsive.

to the Withdrawal 'from transmission of a carrier Wave for actuating thecorresponding signal and means responsive to the condition ofwithdrawalat the saine time oi' a plurality of said carrier Waves oishifting saidinterlocking circuits to prevent the actuation of any of said signalsand to actuate said marginal relay and an indicating device controlledby said marginal relay.

9. In a carrier Wave signaling svstem, a plurality of carrier Wavechannels, signa-ls corresponding to said channels and arranged to becontrolled individually over the respective channels, a signal common toa plnk rality of said channels, and means controlled simultaneously oversaid plurality of channels for actuating said last-mentioned signal.

In Witness whereof, I hereunto subscribe my name this 25th day ofNovember A. D.

WALLACE v. WoLFE;

